A and his girlfriend B were having an affair with another man because of B. Soon A met a girl C and confessed. It turned out that they were still in contact. C what should I do?

If C really loves A, leave decisively. For a man, if two women choose together, the man will choose the one who doesn't care about himself the most. Still the hardest one to chase.

C should be determined to lose and fight it to the death.

AB broke up, so it's impossible to go back easily, otherwise it wouldn't break up. As for friends, everything is temporary. In the future, everyone has their own lives, and there is no way to disturb each other, because they can't face the indifference after the change. I believe you can stick to this relationship. Cherish the present,